The present invention relates to intake air separation systems for internal combustion engines, and more particularly, to an intake air separation system that includes an air separation membrane adapted to produce streams of oxygen enriched air and nitrogen enriched air integrated with a coalescing filter to remove liquids.
Exhaust emission regulations have become increasingly restrictive, and internal combustion engine manufacturers are faced with competing interests in having to meet the emissions requirements while providing acceptable engine performance, including fuel efficiency. Exhaust emissions include visible smoke, particulate matter and oxides of nitrogen (NOx). Particulate matter includes unburned hydrocarbons and soot, while NOx emissions are a somewhat indefinite mixture of oxides of nitrogen, which may include primarily NO and NO2. Many approaches have been used to address emissions issues, including fuel injection, combustion control strategies and systems, after treatment systems and exhaust gas recirculation (EGR) systems.
Attempts at solving one issue can have a negative impact on others. For example, emission reduction systems often have a negative effect on fuel efficiency. To improve fuel efficiency, or power density, it is known to increase the amount of oxygen in the combustion chamber. This has been done in the past by pressurizing the combustion air provided to the combustion chamber. Pressurization of the combustion air increases the oxygen available for combustion. Turbochargers have been used for this purpose.
After treatment of exhaust gas can be used to reduce the amount of unburned hydrocarbons by continuing oxidation of the unburned hydrocarbons. A secondary air supply can be provided to the exhaust stream. The already high temperature of the exhaust stream will support further combustion with the introduction of additional oxygen in the exhaust gas stream. A trade-off occurs in that while particulate matter may be reduced, the further oxidation creates still higher temperatures in the exhaust system. The design of exhaust systems for these higher temperatures requires components able to withstand a much hotter environment. Such components are often heavy and expensive, and may require more frequent servicing.
Decreased fuel consumption and decreased particulate production often go hand-in-hand. However, at the same time, NOx production often increases. NOx forms when nitrogen mixes in a high temperature environment with excess oxygen not used in the combustion process. Therefore, while excess oxygen and high combustion temperatures are beneficial in reducing fuel consumption, the same combination is detrimental in terms of increased NOx formation. Engine manufactures must strike a delicate balance whereby NOx production, fuel consumption and particulate matter formation are controlled to meet emissions regulations and engine user demands.
NOx reduction has been accomplished using exhaust gas recirculation (EGR). By introducing EGR flow to the combustion chamber, the amount of available oxygen for formation of NOx is reduced. By reducing the amount of oxygen, the combustion process is slowed, thereby reducing the peek temperatures in the combustion chamber. EGR systems typically use exhaust gas, but may also use enriched nitrogen sources.
U.S. Pat. No. 6,289,884 xe2x80x9cINTAKE AIR SEPARATION SYSTEM FOR AN INTERNAL COMBUSTION ENGINExe2x80x9d issued Sep. 18, 2001, discloses a method and system for intake air separation in an internal combustion engine. An intake air separation device utilizes a membrane to separate the intake air into a flow of oxygen enriched air and a flow of nitrogen enriched air. A purge air circuit is used to deliver a flow of sweep air or purge air to the intake air separation device, thereby increasing the effectiveness of the air separation.
One of the problems associated with the use of air separation membranes is the accumulation of tiny droplets of fluids (aerosols) on the surfaces of the membranes, with the resultant decrease of separation efficiency. Aerosols can originate from lubrication of upstream equipment, such as compressors, and from the condensation of water or other vapors present in the gas stream being separated. In stationary and process systems that use air separation membrane technology, the problem can be overcome through the use of separate coalescing filters to remove the aerosols upstream of the separation membrane. Known designs for such coalescing filters are large relative to the volume of the air stream being processed, and have large pressure drops associated with the air streams passed therethrough. Because of the filter size and associated pressure drop, use of separate coalescing filters in most engine applications employing air separation membranes has not been practical.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an intake air separation system provides nitrogen enriched air for a combustion process within an internal combustion engine. The intake air separation system is provided with an intake air input adapted to provide intake air used in the combustion process for the engine. An intake air separation device is in flow communication with the intake air input, and is adapted for receiving the intake air and separating the intake air into an oxygen enriched air stream and a nitrogen enriched air stream. The intake air device includes an integral coalescing filter. A permeate outlet is in fluid communication with the intake air separation device, and adapted to receive the oxygen enriched air stream. A retentate outlet is in fluid communication with the intake air separation device and the intake manifold.
In another aspect of the invention, a method of separating an intake air flow in an internal combustion engine having an intake air system adapted for providing intake air to an intake manifold and one or more combustion chambers, has steps of: providing an intake air separation device including a permeation barrier layer; directing the intake air to the intake air separation device; in the air separation device, at the permeation barrier layer, dividing the intake air into an oxygen enriched air stream and a nitrogen enriched air stream; providing a coalescing layer in the intake air separation device for restricting liquid droplets from reaching the permeation barrier layer; and passing liquid droplets from the air separation device with the nitrogen enriched air stream.
In still another aspect of the invention, a gas separation device for separating an incoming gas stream into an first gas constituent stream and a second gas constituent stream is provided with a shell, an inlet in the shell for receiving the incoming gas stream, a permeate outlet from the shell for the first gas constituent stream and a retentate outlet from the shell for the second gas constituent stream. A plurality of fibers are disposed in the shell, each adapted to receive a portion of the incoming gas stream. Each the fiber includes a permeation barrier layer adapted for separating the portion of the incoming gas stream into an first gas constituent stream and a second gas constituent stream, and a coalescing layer restricting the passage of liquid droplets to the permeation barrier layer.
In a yet further aspect of the invention, an internal combustion engine is provided with a combustion section including a plurality of combustion chambers, an exhaust system including an exhaust conduit, an intake manifold, and an intake air separation system adapted for providing a nitrogen enriched air stream for a combustion process within the plurality of combustion chambers. The intake air separation system has an intake air input adapted to provide the intake air used in the combustion process for the engine. An intake air separation device is in flow communication with the intake air input, and is adapted for receiving the intake air and separating the intake air into an oxygen enriched air stream and a nitrogen enriched air stream. The intake air separation device includes an integral coalescing filter. A permeate outlet is in fluid flow communication with the intake air separation device, and is adapted to receive the oxygen enriched air stream. A retentate outlet is in fluid flow communication with the intake air separation device and the intake manifold, and is adapted to provide the nitrogen enriched air stream to the intake manifold for use in the combustion process.